1. Field of the Invention
This invention relates to a builder system for use in detergent products.
2. Description of the Prior Art Practices
Detergent manufacturers have long recognized the need to control water hardness to ensure adequate cleaning by detergents. Even those detergent products which are not particularly hardness sensitive require some detergent builder to prevent the precipitation onto fabrics of water hardness ions particularly at the sites of body soil stains.
The detergency builders employed in the past have been of two main types, namely, sequestering builders and precipitating builders. Sequestering builders are true chelating agents which complex water hardness ions, mainly calcium and magnesium, to lessen the ability of such ions to interfere with the detergency process. Examples of commonly used sequestering builders are the water-soluble salts of pyrophosphates, tripolyphosphates, and nitrilotriacetates. Granular detergent products sold today in the United States contain up to about 50% by weight of the aforementioned phosphate salts. The use of water-soluble phosphate salts as detergency builders has been under criticism because phosphates are believed to accelerate eutrophication, or aging of natural water bodies. Unfortunately, most other sequestering builders are unable to control hardness as effectively as the water-soluble pyrophosphate and tripolyphosphate salts in amounts which are feasible for use in a detergent composition.
Alternatively, some detergent manufacturers have turned to the use of precipitating builders such as the water-soluble salts of carbonates and silicates to achieve water-hardness control. It is noted at this point that while the water-soluble salts of carbonates and silicates are classed as precipitating builders, these materials may also associate with the water-hardness ions in a wash solution.
The presence of soluble carbonates or soluble pyrophosphates, when used separately as builders, results in the deposition of the respective insoluble calcium salts of both upon the washed fabrics.
It has been previously suggested in British Pat. No. 607,274 (Madsen), Canadian Pat. No. 511,607 (Cocks et al.), and Belgian Pat. No. 798,856 (Jacobsen et al.) herein incorporated by reference that the rate of depletion of hardness ions from a wash solution may be increased by the use of crystallization seeds in conjunction with the precipitating builder. The crystallization seeds function as growth sites for the hardness ions and the anion of the precipitating builder. Calcium carbonate crystallization seeds are most desirable in that they are inexpensive and relatively easy to process as well as being an excellent growth site for calcium salts, particularly those having a carbonate anion. The deficiency in using calcium carbonate crystallization seeds in combination with water-soluble carbonates, bicarbonates, and sesquicarbonates is that although the system is very efficient in rapidly reducing the level of soluble calcium, the remainder of the hardness ions present, particularly magnesium, are too soluble to permit precipitation with the aforementioned water-soluble salts. The term "soluble calcium" which is used interchangeably with free calcium ions includes free divalent calcium ions as well as ion pairs, such as monomolecular calcium carbonate, which are in rapid equilibrium with the calcium ion.
In an article, Effect of Impurities on Precipitation of Calcium, by Schonfeld, in the Journal of the American Water Works Association, June 1964, pp. 767-773, it is stated that as little as from 1.5 to 3.0 ppm of sequestering builders such as hexametaphosphate, pyrophosphate, and orthophosphate will effectively negate the ability of as much as 5,000 ppm of a precipitating builder such as sodium carbonate to rapidly remove soluble calcium from solution. It is also known that slightly higher concentrations of materials such as soluble ethylenediaminetetraacetate, ammonium oxylate, sodium tripolyphosphate, and other sequestering builders will also have a substantial effect on the ability of a precipitating builder such as sodium carbonate to deplete free calcium from a wash solution.
It is further known that minute amounts of materials such as the water-soluble pyrophosphates, tripolyphosphates, and other sequestering builders will upon intimate contact with the calcium carbonate crystallization seeds render the seeds ineffective in accelerating the rate of calcium depletion. Stated otherwise, sequestering builders poison the crystallization seeds to such an extent that the precipitating builder effectively functions alone. The amount of sequestering builder or similar material which render the calcium carbonate crystallization seed ineffective will vary with the type of material, i.e., sequestering builder employed. It is generally sufficient to say that when the sequestering builder or the inhibiting material is in intimate contact with the calcium carbonate crystallization seed that as little as 1.5 ppm is sufficient to poison the crystallization seed rendering it ineffective. For instance, 1.5 ppm of sodium pyrophosphate in an aqueous slurry is sufficient to adsorb over the entire surface area of a 0.25 micron calcium carbonate crystallization seed which is present at 60 ppm. Since the crystallization seed level above corresponds to 5% by weight in a typical detergent product when used at suggested levels, it would appear necessary to reduce the level of phosphate to the point at which it would be ineffective as a builder in a detergent product.
Alkali metal silicates are also known to adsorb onto calcium carbonate particles to render the latter ineffective as a crystallization seed. The aforementioned silicates are also desirable in detergent compositions to prevent washing machine corrosion and to aid in detergency. Alkali metal silicates are generally classed as precipitating builder salts.
It has been discovered that it is possible to formulate a detergent builder system or complete detergent product utilizing a crystallization seed, a precipitating builder, namely water-soluble carbonates, bicarbonates, or sesquicarbonates, a sequestering builder, and an alkali metal silicate. Contrary to what one would expect from the prior art, it has been found that substantial amounts of sequestering builders such as water-soluble salts of pyrophosphates, tripolyphosphates, nitrilotriacetates, and an alkali metal silicate may be present in a wash solution at the same time as the calcium carbonate crystallization seed and the aforementioned precipitating builder salts without substantially interfering with the removal of soluble calcium by precipitation. While some effect on the precipitation of soluble calcium will occur from the use of the sequestering builders, it is much less than one would predict upon comparing the individual effect of these builders upon systems containing the aforementioned precipitating builder salts or the separate effect on the growth of crystallization seeds such as is observed in the processes for the manufacture of commercial calcium carbonate.
It has been surprisingly discovered that the benefits of the present invention in maintaining calcium and magnesium ion control in the wash solution allows for satisfactory detergency results in low or no phosphate detergent compositions.
Another advantage to the present invention in its low phosphate aspect compared to non-phosphate detergent products is that the former gives granules which are more resistant to humidity caking.
The benefits of the present invention in its non-phosphate aspect allow the use of expensive sequestering builders at amounts much lower than would otherwise be required to achieve water-hardness control. In the case of non-phosphate compositions of the present invention it is also possible to use sequestering builders which are economically attractive but which lack the water-hardness sequestration ability of the water-soluble pyrophosphates and tripolyphosphates.
It has also been observed that water-soluble pyrophosphates may be incorporated in the present invention without substantial calcium pyrophosphate precipitation upon fabrics. Pyrophosphate may be present as a builder or from reversion of higher polyphosphate species. Similarly, calcium carbonate deposition upon fabrics is greatly diminished in the present invention despite the addition of large amounts of calcium carbonate particles.
In the concurrently filled, commonly assigned application of Everett J. Collier entitled BUILDER SYSTEM AND DETERGENT PRODUCT, Ser. No. 509,865, herein incorporated by reference, it is recognized that the sequestering builder need not be delayed from entering solution until after the precipitating builder and crystallization seed have functioned. While the composition performs adequately without such delay, it has been found that better performance is obtained when delay is accomplished by the manner hereinafter described. Delaying the solution of the granule containing the sequestering builder is accomplished by including in the slurry from which the granule is formed an amount of alkali metal silicate of the formula M.sub.2 O:SiO.sub.2 with the ratio being from about 1:2 to about 1:3.75 where M is the alkali metal. Ordinarily the M.sub.2 O:SiO.sub.2 ratio in detergent products is from 1:1 to 1:2.4. Additionally, the alkali metal silicate in the product at the aforementioned ratios does not substantially interfere with the crystallization seed in the wash.
Throughout the specification and claims, percentages and ratios are given by weight unless otherwise indicated and temperatures are in Fahrenheit degrees.